1. Field of the Invention
The present invention relates to the field of earplugs and more particularly to the field of molded foam earplugs.
2. Description of the Prior Art
Foam earplugs have been developed which fit comfortably in the ear and provide desired sound attenuation. Examples of these earplugs are disclosed in U.S. Pat. No. 3,811,437 to Ross Gardner, Jr. which later reissued as U.S. Pat. No. Re. 29,487. Gardner teaches that a variety of resilient polymeric foams can be used. The foam has a sufficiently high concentration of organic plasticizer which permits the plug to be compressed and inserted into the ear canal. After insertion the plug recovers to exert an equilibrium pressure within the comfort range of the wearer. Louis Wood in his U.S. Pat. No. 4,158,087 discloses a polyurethane, latex foam which can be used for foam earplugs. Following the teaching of these patents, several companies have made and sold resilient foam earplugs.
Resilient foam earplugs have been made in a variety of shapes. Cylindrical earplugs are commonly used as are generally conical, and bullet-shaped plugs. The bullet-shaped plugs are sometimes provided with a concave flanged base which does not go into the ear canal. The only constraint to the shape of the plug is that the plug must be able to be compressed to a size smaller than the ear canal so that the plug can be inserted into the ear canal, there expand to seal the ear canal and exert a comfortable, yet effective, pressure against the wall of the ear canal.
Foam earplugs have been punched from sheets of foam and molded. In order to produce an earplug with a contoured shape, it is preferable that the plug be formed in a mold. Cantor in U.S. Pat. No. 2,441,866 discloses a bullet shaped rubber earplug having a hollow interior. The Cantor earplug cannot be radially compressed. If one exerts a radial force on the Cantor earplug, the wall of the earplug will bulge in a direction normal to the force or the wall will buckle. In either event, the circumference of the earplug will not change. A bulged Cantor earplug cannot be inserted into the ear canal unless it buckles. If a buckled Cantor earplug is inserted into the ear canal, the buckle will remain and the ear canal will not be completely sealed. Cabot Corporation has made and sold a foam earplug similar in shape to the Cantor rubber earplug. Like Cantor, this was a push-in type plug that could not be radially compressed for insertion into an ear canal.
When a foam earplug is formed in a mold, there is a tendency for the foam to adhere to the mold surface and remain in the cavity of the mold. This tendency prevents easy removal of the molded foam from the mold cavity after formation. The use of pins which are suspended from a top plate and inserted into the cavity of the mold have been tried for some kinds of molded products. However, all too frequently, the pin will tear the molded product during removal from the mold. The art has not used pins in the molding of earplugs. Nor has the art recognized that pins of certain dimensions can be used to create a beneficial cavity in a molded slow recovery foam earplug.